Q. Watching “The Love Boat” episodes on a cable TV retro channel made me wonder: Was cruising popular before Julie, Doc, Gopher, Isaac and the Captain sailed on the airwaves — or did they actually launch the craze?

— B.Z., of Millstadt

A. Some joke — it was the longest-running TV infomercial and the most effective subliminal messaging in history. But whether you liked the sappy sitcom or not, “The Love Boat” played a crucial role in raising the anchor on the cruise ship industry after the show debuted in 1977, according to those in the business.

“‘The Love Boat’ was the tipping point, the fulcrum that transformed the entire cruise industry,” Bob Dickinson, of Carnival Cruise Lines, told TheTravelMavens.com a couple of years ago. “That show put cruising on the map. It moved cruising into the national psyche.”

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Cruising has been around since 1844, when the Peninsular & Oriental Steam Navigation Co. began advertising sea tours from Southampton, England, to such exotic locales as Gibraltar, Malta and Athens. When the idea caught on, the company began building bigger and more luxurious ships during the second half of 19th century, including the SS Valetta in 1889, the first ship to use electric lights.

By the turn of the century, companies were steaming full speed ahead as more people wanted to cross the Atlantic in comfort. European companies more than doubled their fleet of luxury liners. Eventually, it would lead to the White Star’s Olympic-class liners: the Olympic, the Britannic — and the Titanic.

But with the arrival of modern jet aircraft in the 1960s, ocean travel dropped precipitously. Not only were planes faster, but older ocean liners also were a far cry from the floating palaces they are today: They guzzled fuel, they could not enter shallow ports and their cabins — often windowless — were designed to maximize capacity, not comfort.

One of the first attempts to turn things around came in 1974, when the Cunard Line announced two revolutionary changes to its flagship, the Queen Elizabeth II. For one, it began hiring international celebrities to perform and advertised the four-day Atlantic crossing as a vacation-entertainment experience. Perhaps equally enticing, it introduced “one-class” cruising with all passengers eligible for the same service, menus, entertainment and activities. It soon spurred people into thinking of cruising as a vacation in itself rather than a means of getting somewhere.

But it was perhaps “The Love Boat” that sealed the deal as, for 10 years, viewers imagined themselves being pampered by an ever-attentive crew as they sailed the balmy seas on a romantic getaway. The show also would put Princess Cruises on the map. In 1962, founder Stanley McDonald fell in love with the idea of cruising while visiting the 1962 Seattle World’s Fair. So, three years later, he chartered Canadian Pacific Limited’s Princess Patricia during the ship’s off-season to make runs from L.A. to Acapulco.

Soon, McDonald’s new company began adding more ships. These included the Princess Carla, on which Jennifer Saunders would write the first chapters of her book “The Love Boats,” detailing her recollections as a hostess on a cruise ship. Then, in 1974, the Island Princess and Pacific Princess became part of the Princess fleet. Finally, in 1977, all the pieces came together when TV producer Douglas Cramer rejuvenated his old “Love, American Style” series by putting it on a modern cruise ship. So he borrowed Saunders’ experiences and filmed the pilot aboard the Sun Princess in Mexico. For the next decade, it would be one of the highest-rated shows on TV as Gavin McLeod and his crew took viewers around the world aboard the Island Princess and Pacific Princess.

At first, the ships were relatively small and the trips expensive. The Pacific Princess, for example, weighed only 20,000 tons, carried just 650 passengers and cost up to $5,000 a week.

“We still had a negative halo,” Dickinson said. “Cruising had the image of an elitist vacation.”

But as more companies saw the coming craze, ships grew in size and costs plummeted. Today, Royal Caribbean’s Allure of the Seas and Ocean of the Seas weigh 225,000 tons each and can carry more than 6,000 passengers. With that kind of capacity, you can imagine the growth in demand. In 1970, an estimated 500,000 people took a cruise. By 1990, it had climbed to nearly 4 million. Now, thanks ironically to another push from the 1997 movie “Titanic,” passengers have more than quintupled in 25 years to 21 million annually. At the same time, costs have tumbled from about $500 a day in the 1980s to $100 a day today. The industry now employs 314,000 and adds nearly $38 billion to the U.S. economy.

No wonder they called it “The Love Boat.”

Today’s trivia

What has become of the Pacific Princess from “The Love Boat”?

Answer to Sunday’s trivia: If you’ve ever seen the popular 1968 cult movie “Barbarella,” you know that our heroine (played by Jane Fonda) was given the task of retrieving a Dr. Durand Durand from the Tau Ceti region in space because he had invented the Positronic Ray and Earth leaders feared it might fall into the wrong hands. Fast forward to Birmingham, England, in 1978, when musicians John Taylor and Nick Rhodes became the resident band at the Rum Runner, which was near the city’s nightclub of note — Barbarella’s — where such bands as The Sex Pistols and The Clash often played. As a result, Taylor and Rhodes named their band Duran Duran after the movie character played by Milo O’Shea. Now the band has a star on the Hollywood Walk of Fame after a string of 1980s hits that included “Rio,” “Union of the Snake” and “Hungry Like the Wolf” with those unforgettable shrieks at the end from Rhodes’ girlfriend at the time.